So after a Pm to a very generous BlackSox, Tourok and I have put another 7 or so levels on the enderman farm, and Tourok gave it a much needed service as well - blocks had a habit of becoming out of place (were still arguing over why!) which meant endermen could spawn and not be knocked down.

The end result of all this?

Level 50 xp in less than 10 minutes - the spawn rate is high and constant, so you never get to the point where you are waiting for them to build up again.
Instructions:
1. Make sure it's your turn
2. Start bashing!
3. Repeat 2 until you reach desired level.

Just chuck them in the lava incinerator... by the time you walk there and back, more endermen have gathered, so it's win win.

Not a chance. Last time I tried that I absentmindedly right clicked with an Ender Perl in my hand and was promptly teleported into the incinerator -- which was oh so delighted to simply incinerated me and my 40 XP. I don't touch the evil things now while down there. Not even if there's a tiny spinning gerbil inside.